Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing an embodiment of the new design;

FIG. 2 is a second embodiment thereof;

FIG. 3 is a third embodiment thereof; and,

FIG. 4 is a fourth embodiment thereof.

The dotted lines showing portions of the graphical user interface illustrate environmental subject matter and form no part of the claimed design.

The dash-dot-dash line showing of a display screen or portion thereof defines the bounds of the claimed design and forms no part thereof. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 